Diesel engines typically rely on compression ignition, where fuel is injected into a combustion chamber after air has been compressed, resulting in substantially immediate combustion without requiring a sparkplug. Compression ignition diesel engines typically include a common rail fuel injection system, which directs pressurized fuel to individual fuel injectors for injection into the combustion chamber. Prior to entering the common rail, fuel is typically pumped through a primary filter and a secondary filter by a feed pump located between the filters. A high-pressure pump is typically located downstream of the secondary filter.
In typical systems, a regulator valve positioned between the secondary filter and the high-pressure pump returns excess fuel (i.e., fuel in excess of a capacity of the high-pressure pump) to the inlet of the feed pump. Therefore, more fuel than necessary passes through the secondary filter, reducing the useful life of the secondary filter or otherwise requiring the secondary filter to be designed larger than necessary to handle the excess flow without reducing the useful life.
One attempt at preventing unnecessary flow across a filter of a fuel injection system is described in U.S. Pat. No. 6,520,162 (the '162 patent) issued to Schueler. The '162 patent discloses a common rail system provided with a pre-feed pump for delivering a fuel flow from a fuel tank to a high-pressure pump. The '162 patent also discloses a fuel filter disposed downstream of the pre-feed pump and a safety valve device that is dependent on a fuel filter pressure difference for shutting off flow through the filter, and a bypass to circumvent the safety valve device.
Although the fuel injection system of the '162 patent may provide a method for protecting a fuel pump from damage due to abnormal conditions, it fails to provide a method for controlling fuel flow during normal conditions. Specifically, the '162 patent fails to prevent unnecessary flow across a fuel filter during normal operating conditions to extend the useful life of the filter or to allow for a smaller filter design area.
The present disclosure is directed to overcoming one or more of the problems set forth above.